Unique Response to Heat of Extracellular Protease of Pseudomonas fluorescens M5

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Abstract
Eight proteases selected from 38 cultures of psychrotrophic bacteria were subjected to heat stability tests. Cell-free filtrates of the broth in which the cultures were grown individually were heated to 40, 50, 60 and 70.degree. C for 0, 15, 30 and 60 min. Six of the filtrates were less than 50% inactivated by heating at 40.degree. C for 60 min; the enzyme of P. fluorescens M5 was inactivated completely by this treatment. Of the 5 most proteolytic cultures tested, including P. flourescens M5, losses in protease activity ranged from 9-34% on heating at 70.degree. C for 60 min. Purified M5 protease retained at least 75% of its activity over the pH range of 4.5-7.5. Electrophoresis of active M5 protesase from 4 chromatographed fractions revealed 2 hands in each with approximate MW of 35,000 and 45,000. Heating at 40.degree. C did not alter mobility of either band. Reasons for lability at 40.degree. C but stability at 50, 60 and 70.degree. C are discussed. Complexation with casein, observed with another protease, was not a possible explanation for stability at 40.degree. C.